Chains of 1000 granules in mutual contact, without precompression, and with random radii that follow a normal distribution are studied numerically. The standard deviation $\sigma$ controls the disorder level. The chains are subject to (i) a striker impact and (ii) an actuator that imposes band-limited white-noise motion at one boundary. For striker excitation, a critical ${\sigma }_c\approx 0.1$ separates weak and strong disorder, and the propagation of the median peak momentum exhibits two regimes: (i) for short distances, a $\sigma$-dependent decay, and (ii), at long distances, a universal power law $\propto k^{-0.83}$, where $k$ denotes the granule position. For actuator excitation, the transfer function reveals a transition from a low-pass response, at $\sigma <0.3$, to broadband mechanical noise suppression for higher disorder levels. The narrow passbands at a few hundred hertz that we observe are consistent with the preferred transmission bands in soils reported experimentally in the literature. Thus, simple disordered granular chains provide a minimal model to investigate selective transmission or attenuation in random granular media. The findings are relevant to near-surface site characterization, shallow buried-object detection, and related geophysical applications.

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• Acoustic wave phenomena
• Noise
• Sound waves
• Ultrasound attenuation
• Granular chains
• Granular materials
• Traveling waves